A method and a device for the optical scanning of a document by means of a line camera in which the document may be scanned at variable speed. Since on the one hand a line frequency by which the individual lines are scanned is based on the speed of movement, and on the other hand binning is carried out automatically on the basis of the speed of movement, wherein the line frequency is multiplied by a binning factor n, it is possible for a document to be scanned very easily and simply over a wide speed range. Color values are preferably corrected by means of an amplification factor, so that the brightness of the images produced by this means is constant over the whole speed range.
Legal claims defining the scope of protection, as filed with the USPTO.
1. Method for the optical scanning of a document with a line camera, the method comprising: moving the line camera during scanning relative to the document at a speed of movement, wherein during scanning at a predetermined nominal speed and a predetermined nominal line frequency an output image with a nominal resolution is generated, and that the scanning of the document is effected at a variable speed of movement wherein a line frequency at which individual lines are scanned is changed in proportion to the speed of movement and when the speed of movement is reduced by a predetermined amount relative to the nominal speed, color values of several lines are averaged to give one color value and the line frequency is proportional to a product of speed of movement and a number of color values to be averaged, wherein depending on the speed of movement, the number of color values to be averaged is changed automatically.
2. Method according to claim 1 , wherein the color values are amplified by an amplification factor which is indirectly proportional to the speed of movement for a speed range in which a specific number of color values are averaged, wherein this number is described as a binning factor.
3. Method according to claim 2 , wherein the amplification factor is proportional to a ratio between the speed of movement and the nominal speed multiplied by the binning factor.
4. Method according to claim 3 , wherein the number of color values to be averaged in each case is a power of 2.
5. Method according to claim 4 , wherein the number of color values to be averaged extends over a range of 1-32, or 1-128 or 1-1024.
6. Method according to claim 5 , wherein the line frequency lies in a range of 500 Hz to 50 KHz.
7. Method according to claim 6 , wherein the document is scanned at a speed of movement greater than the nominal speed, while the resolution of images produced is reduced in a direction of movement.
8. Method according to claim 7 , wherein, as the speed of movement is increased, the resolution is reduced in steps, and in the separate resolution reduction steps the line frequency is changed in proportion to the speed of movement.
9. Method according to claim 7 , wherein during scanning by a CCD with several scan lines, on account of an offset of the scan lines, a correction of a spacing between two lines is made, wherein this line spacing is divided by a reduction factor.
10. Method according to claim 9 , wherein in a further reduction of speed of movement, only each i th scanned line is used.
11. Method according to claim 10 , wherein with increased reduction in the speed of movement, a number i is increased step by step, and in the separate steps the line frequency is changed in proportion to the speed of movement.
12. Method according to claim 11 , wherein for i, only powers of 2 are used.
13. Method according to claim 12 , wherein the line camera has at least two parallel scan lines arranged at a distance s from one another, and a lens with an image scale M, wherein the following steps are taken: line-by-line scanning of the document by the line camera, wherein by means of each scan line a separate image of the document is produced, these images being offset from one another according to the distance s between the scan lines, and divided into a multiplicity of lines, wherein a distance D between two adjacent lines of an image in an image plane of the line camera amounts to D = v t · t z M wherein v t is a speed at which the line camera is moved relative to an object, and t z is a period of time between two consecutive exposures by one of the scan lines, so that an offset Z of the images in a unit of the line spacing D results in Z=s/D, bringing into congruence of the images by shifting at least one of the images relative to the other image by Int(Z) lines to reduce the offset, and interpolation of one of the images with lines offset by (Z-Int(Z)).
14. Method according to claim 13 , wherein the line camera has more than two scan lines, each of which produces an image, wherein all images are brought into congruence.
15. Method according to claim 14 , wherein the scan lines are designed to detect different colors.
16. Method according to claim 15 , wherein one of the scan lines is designed to detect a specific color, and that the images generated by the other scan lines are interpolated so as to be brought into congruence with the image of the specific color.
17. Method according to claim 16 , wherein the specific color is green.
18. Method according to claim 17 , wherein during interpolation in each case two color separation values of adjacent image lines are interpolated with one another, wherein one of the two color separation values is weighted by a decimal place content of Z, and the other color separation value is weighted by one minus the decimal place content of Z.
19. Method according to claim 18 , wherein the method is executed line by line, i.e. that when one or two image lines of each image are produced, they are brought into congruence with corresponding image lines of the other images.
20. Method according to claim 19 , wherein the offset Z is calculated on the basis of an optical resolution of a system comprising line camera and lens in a line direction, a movement resolution dependent on speed and by which the line camera is moved relative to the object, and a number z which is a distance between two adjacent scan lines of the line camera in units of a pitch width of adjacent sensor elements of a scan line.
21. Method according to claim 1 , wherein the number of color values to be averaged in each case is a power of 2.
22. Method according to claim 1 , wherein the number of color values to be averaged extends over a range of 1-32, or 1-128 or 1-1024.
23. Method according to claim 1 , wherein the line frequency lies in a range of 500 Hz to 50 KHz.
24. Method according to claim 1 , wherein the document is scanned at a speed of movement greater than the nominal speed, while in this case the resolution of the images produced is reduced in a direction of movement.
25. Method according to claim 24 , wherein, as the speed of movement is increased, the resolution is reduced in steps, and in the separate resolution reduction steps the line frequency is changed in proportion to the speed of movement.
26. Method according to claim 24 , wherein during scanning by a CCD with several scan lines, on account of an offset of the scan lines, a correction of the spacing between two lines is made, wherein this line spacing is divided by a reduction factor.
27. Method according to claim 1 , wherein in a further reduction of speed of movement, only each i th scanned line is used.
28. Method according to claim 27 , wherein with increased reduction in the speed of movement, a number i is increased step by step, and in the separate steps the line frequency is changed in proportion to the speed of movement.
29. Method according to claim 27 , wherein for i, only powers of 2 are used.
30. Method according to claim 1 , wherein the line camera has at least two parallel scan lines arranged at a distance s from one another, and a lens with an image scale M, wherein the following steps are taken: line-by-line scanning of the document by the line camera, wherein by means of each scan line a separate image of the document is produced, these images being offset from one another according to the distance s between the scan lines, and divided into a multiplicity of lines, wherein a distance D between two adjacent lines of an image in an image plane of the line camera amounts to D = v t · t z M wherein v t is the speed at which the line camera is moved relative to the object, and t z is a period of time between two consecutive exposures by one of the scan lines, so that an offset Z of the images in a unit of the line spacing D results in Z=s/D, bringing into congruence of the images by shifting at least one of the images relative to the other image by Int(Z) lines to reduce the offset, and interpolation of one of the images with lines offset by (Z-Int(Z)).
31. Method according to claim 30 , wherein the line camera has more than two scan lines, each of which produces an image, wherein all images are brought into congruence.
32. Method according to claim 30 , wherein the scan lines are designed to detect different colors.
33. Method according to claim 32 , wherein one of the scan lines is designed to detect a specific color, and that the images generated by the other scan lines are interpolated so as to be brought into congruence with the image of the specific color.
34. Method according to claim 33 , wherein the specific color is green.
35. Method according to claim 34 , wherein during interpolation in each case two color separation values of adjacent image lines are interpolated with one another, wherein one of the two color separation values is weighted by a decimal place content of Z, and the other color separation value is weighted by one minus the decimal place content of Z.
36. Method according to any of claim 30 , wherein the method is executed line by line, i.e. that when one or two image lines of each image are produced, they are brought into congruence with a corresponding image lines of the other images.
37. Method according to claim 30 , wherein the offset Z is calculated on the basis of an optical resolution of a system comprising line camera and lens in the line direction, a movement resolution dependent on speed and by which the line camera is moved relative to the document, and a number z which gives a distance between two adjacent scan lines of the line camera in units of a pitch width of adjacent sensor elements of a scan line.
38. Device for the optical scanning, comprising: a sensor unit including a line camera with a CCD and a lens; an input control element with an input for the connection of an encoder by which a relative speed between the line camera and a document to be scanned is detected; and a signal processor, wherein the input control element and the signal processor execute the method for optical scanning of a document by means of a line camera which, during scanning, is moved relative to the document at a speed of movement, wherein during scanning at a predetermined nominal speed and a predetermined nominal line frequency an image with a nominal resolution is generated, and that the scanning of the document is effected at a variable speed of movement wherein a line frequency at which in each case individual lines are scanned is changed in proportion to the speed of movement and that when the speed of movement is reduced by a predetermined amount relative to the nominal speed, color values of several lines are in each case averaged to give one color value (binning) and the line frequency is proportional to a product of speed of movement and a number of color values to be averaged, so that even at reduced speed an image with nominal resolution is generated, wherein depending on the speed of movement, the number of color values to be averaged in each case is changed automatically.
39. Device according to claim 38 , wherein the input control element and the signal processor are formed by an FPGA.
40. Device according to claim 39 , wherein the device is a camera module which may be retrofitted to an existing scanning system.
41. Device according to claim 38 , wherein the device is a camera module which may be retrofitted to an existing scanning system.
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August 27, 2007
July 26, 2011
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